Is there a way to estimate blood concentration of a drug in the arm
and hand based on a specific rate of infusion, e.g., ug/min, of that
drug via the brachial artery?

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Request for Question Clarification by synarchy-ga on 10 Mar 2003 18:31 PST

Is this question in regard to a known drug - if so, there might well
be a known method of approximation of the distribution of the drug.

If the question is regarding an unknown drug, or a substance in
general, the question becomes more problematic for the all of the
reasons suggested in the comments (ie rate of distribution, rate of
clearance, rate of metabolism/breakdown, rate of protein binding,
etc.).

Also, where in arm and hand are you wanting to know the concentration?
 Intravascularly (reasonably easy), extracellularly (could be easy,
depends on drug), intracellularly in the tissues of the hand (much
more difficult, largely dependent upon the drug), or within a wound
(difficult, hugely dependent upon the drug).

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Clarification of Question by carver-ga on 11 Mar 2003 11:18 PST

The drug in question is clonidine.  It is being infused into the
brachial artery at a rate of 1 microgram/min for 5 min.  I would like
an estimate of the intravascular and extracellular concentrations in
the hand at the end of the 5 min.

Thanks for the help!

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Request for Question Clarification by synarchy-ga on 12 Mar 2003 12:38 PST

Hello - to keep you updated - 

I think that I've found the information that you requested - however,
the journals are not available to me online - I'm trekking down to the
library to make sure that they contain the info that you want.

synarchy

According to my friend, a licensed pharmacist, there is a way.  She
suggested you review sites resulting from a search of the term
"pharmacokinetics" which is "the study of the bodily absorption,
distribution, metabolism, and excretion of drugs."

I searched the term for you in conjunction with brachial monitoring
but I have a limited understanding of pharmaceuticals and medicine and
I do not feel I can accurately review the information I discovered.  I
hope a Researcher with a greater pharmaceutics understanding will be
able to assist you.

Good luck!

SEARCH STRATEGY:

[phone call to pharmacist friend]
pharmacokinetics
pharmacokinetics brachial monitor
pharmacokinetics brachial monitoring

My girlfriend is a nurse. I'll ask her this evening...

This is not a simple question.
First, the intention of arterial injection is to cause the rapid
distribution of a drug throughout the body and o the site of action or
metabolisation in the case of a prodrug (except in the case of
isolated limb perfusion).  Therefore, the blood concentration in the
hand/arm, should very soon be equal to that elsewhere in the body.  In
the case of infusion, this level should rise slowly and uniformly.
As a first approximation ONLY, the blood concentration will be the
total mass of drug delivered divided by the total blood volume.  Now
the aspects of pharmacokinetics and pharmacodynamics enter the
picture.  How fast is the drug withdrawn from the blood system by,
say, the kidney?  How fast does it spontaneously break-down?  How
rapidly is it metabolised by, say, the liver?  Is it preferentially
absorbed by any other organ, for instance, muscle?
In actuality, these parameters cannot be calculated in advance, and
estimates depend upon experimentation, usually initially in animal
studies, and subsequently in Phase I clinical trials.

You may find this page helpful:
http://www.rxlist.com/cgi/generic/clonidin_cp.htm